Auto-injector

ABSTRACT

An auto-injector comprising an elongate housing containing a syringe. The housing having a an orifice intended to be applied against an injection site. The syringe is slidably arranged with respect to the housing. A spring pushing the needle from a covered position into an advanced position, operating the syringe and covering the needle. An activator arranged to lock the spring prior to manual operation and capable of, upon manual operation, releasing the spring means for injection. A first gear arrangement and a second gear arrangement arranged for converting torque from a first end and a second end of the torsion spring into a translative force. The first end groundable in the housing while the second end acts on a plunger through the second gear arrangement for advancing the needle and supplying the dose.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase Application pursuant to35 U.S.C. §371 of International Application No. PCT/EP2011/073508 filedDec. 21, 2011, which claims priority to European Patent Application No.10196073.0 filed Dec. 21, 2010 and U.S. Provisional Patent ApplicationNo. 61/432,241 filed Jan. 13, 2011. The entire disclosure contents ofthese applications are herewith incorporated by reference into thepresent application.

FIELD OF INVENTION

The invention relates to an auto-injector for administering a dose of aliquid medicament according to the preamble of claim 1 and to a methodfor operating the auto-injector according to claim 13.

BACKGROUND

Administering an injection is a process which presents a number of risksand challenges for users and healthcare professionals, both mental andphysical.

Injection devices (i.e. devices capable of delivering medicaments from amedication container) typically fall into two categories—manual devicesand auto-injectors.

In a manual device—the user must provide the mechanical energy to drivethe fluid through the needle. This is typically done by some form ofbutton/plunger that has to be continuously pressed by the user duringthe injection. There are numerous disadvantages to the user from thisapproach. If the user stops pressing the button/plunger then theinjection will also stop. This means that the user can deliver anunderdose if the device is not used properly (i.e. the plunger is notfully pressed to its end position). Injection forces may be too high forthe user, in particular if the patient is elderly or has dexterityproblems.

The extension of the button/plunger may be too great. Thus it can beinconvenient for the user to reach a fully extended button. Thecombination of injection force and button extension can causetrembling/shaking of the hand which in turn increases discomfort as theinserted needle moves.

Auto-injector devices aim to make self-administration of injectedtherapies easier for patients. Current therapies delivered by means ofself-administered injections include drugs for diabetes (both insulinand newer GLP-1 class drugs), migraine, hormone therapies,anticoagulants etc.

Auto-injectors are devices which completely or partially replaceactivities involved in parenteral drug delivery from standard syringes.These activities may include removal of a protective syringe cap,insertion of a needle into a patient's skin, injection of themedicament, removal of the needle, shielding of the needle andpreventing reuse of the device. This overcomes many of the disadvantagesof manual devices. Injection forces/button extension, hand-shaking andthe likelihood of delivering an incomplete dose are reduced. Triggeringmay be performed by numerous means, for example a trigger button or theaction of the needle reaching its injection depth. In some devices theenergy to deliver the fluid is provided by a spring.

US 2002/0095120 A1 discloses an automatic injection device whichautomatically injects a pre-measured quantity of fluid medicine when atension spring is released. The tension spring moves an ampoule and theinjection needle from a storage position to a deployed position when itis released. The content of the ampoule is thereafter expelled by thetension spring forcing a piston forward inside the ampoule. After thefluid medicine has been injected, torsion stored in the tension springis released and the injection needle is automatically retracted back toits original storage position.

SUMMARY

It is an object of the present invention to provide an improvedauto-injector and an improved method for operating it.

The object is achieved by an auto-injector according to claim 1 and by amethod according to claim 14.

Preferred embodiments of the invention are given in the dependentclaims.

In the context of this specification the term proximal refers to thedirection pointing towards the patient during an injection while theterm distal refers to the opposite direction pointing away from thepatient.

An auto-injector for administering a dose of a liquid medicamentaccording to the invention comprises:

-   -   an elongate housing arranged to contain a syringe with a hollow        needle and a stopper for sealing the syringe and displacing the        medicament, the elongate housing having a distal end and a        proximal end with an orifice intended to be applied against an        injection site, wherein the syringe is slidably arranged with        respect to the housing,    -   spring means capable of, upon activation, pushing the needle        from a covered position inside the housing into an advanced        position through the orifice and past the proximal end,        operating the syringe to supply the dose of medicament, and        covering the needle on removal of the auto-injector from the        injection site,    -   activating means arranged to lock the spring means in a        pressurized state prior to manual operation and capable of, upon        manual operation, releasing the spring means for injection.

According to the invention the spring means is a single torsion spring.

In one embodiment a first gear arrangement and a second gear arrangementare arranged for respectively converting torque from a first end and asecond end of the torsion spring into a translative force. The first endis arranged to be groundable in the housing while the second end isconfigured to act on a plunger through the second gear arrangement foradvancing the needle and supplying the dose. The activating means isarranged to block or release the second gear arrangement. When thesecond gear arrangement is blocked by the activating means the torquefrom the second end of the torsion spring is also statically resolved inthe housing. The first end is releasable from the ground in the housingfor causing a translation through the first gear arrangement resultingin the needle getting covered.

This translation may be a needle retraction or preferably theadvancement of a needle shroud over the needle.

The single torsion spring is used for both, inserting the needle andfully emptying the syringe. A major advantage of the torsion spring withgear arrangements is that force is exerted on the stopper and syringe ina smooth manner, whereas a conventional compression spring exhibits arather abrupt force deployment which may spoil a glass syringe or otherparts of the auto-injector.

The needle shroud may be arranged in the housing surrounding the syringeand translatable in longitudinal direction, wherein the needle shroud iscoupled to the first gear arrangement in a manner to be translated inproximal direction over the advanced needle on release of the first endfrom the ground in the housing.

The torque required to advance the needle shroud may be configured to beless than the torque required to advance the plunger and the stopper.This allows for triggering the shroud advancement at any point duringinjection without having to ground the second end of the torsion springin the housing while injection is immediately stopped.

The first gear arrangement and the second gear arrangement mayrespectively comprise a first gear member coupled to the respective endof the torsion spring, wherein the first gear member is engaged througha screw thread to a respective second gear member arranged to translateon rotation of the first gear member.

The needle shroud may be arranged to be in an initial positionprotruding from the proximal end of the housing in an initial stateinterlocked to the activating means for preventing manual operation. Theneedle shroud may be arranged to be translated in distal direction intothe housing into a distal position against the load of a shroud springwhen pushed against the injection site. The needle shroud isrotationally fixed to the housing and to the second gear member of thefirst gear arrangement. In the distal position the needle shroud isarranged to rotationally fix the first gear member to the second gearmember of the first gear arrangement and to allow operation of theactivating means. The needle shroud is thus used as a skin interlockmeans requiring a sequence of operation in order to increase needlesafety. Furthermore, the needle shroud serves for blocking the firstgear arrangement as long as it is maintained pressed against theinjection site. When removed from the skin, the needle shroud returnsinto the initial position under load of the shroud spring therebyreleasing the first gear arrangement for advancing the needle shroudfurther.

The activating means may be arranged to be in a splined engagement withthe first gear member of the first gear arrangement in the initial stateso as to rotationally fix it to the housing, wherein the activatingmeans is arranged to remove this splined engagement on manual operation.This ensures that the first end of the torsion spring is grounded in thehousing prior to injection. The activating means cannot be operatedbefore the needle shroud has been depressed. On depression of the needleshroud the already grounded first end of the torsion spring becomesfurther grounded in the housing through the first gear arrangement.Operating the activating means removes only one of these grounds. Thisensures that the needle shroud is only advanced over the needle when theneedle shroud is allowed to return to the initial position on removalfrom the injection site after an injection has been triggered.

A clip arrangement may be provided comprising at least one resilientchassis clip attached to the housing. The chassis clip may be engageableproximally behind a shoulder in the plunger in a manner to preventtranslation of the plunger in proximal direction. The shoulder may bearranged to flex the chassis clip outwards due to ramped engagementunder force in proximal direction applied to the plunger from the secondend of the torsion spring through the second gear arrangement. Theactivation means may comprise an end trigger button arranged at thedistal end translatable between a distal position and a proximalposition. At least one trigger beam may be arranged on the triggerbutton in a manner to outwardly support the chassis clip to prevent itfrom being outwardly deflected when the end trigger button is in thedistal position. The trigger beam is arranged to be repositioned ontranslation of the end trigger button into the proximal position, i.e.depression in a manner to allow outward deflection of the chassis clipthus releasing the plunger for needle insertion and injection. The endtrigger button may protrude from the distal end in a manner to beaccessible for operation.

At least one flexible first beam element may be arranged on the housing,the flexible first beam element arranged to obstruct the path of the endtrigger button so as to prevent its depression. A second beam element isarranged on the needle shroud in a manner to deflect the flexible firstbeam element out of the path of the end trigger button on depression ofthe needle shroud. This embodiment requires the user to first depressthe needle shroud before the end trigger button can be translated.

In another embodiment a rib may be arranged in the housing in a mannerto obstruct the path of a resilient part of the end trigger button so asto prevent depression of the end trigger button. A lateral triggerbutton may be laterally arranged on the housing arranged to inwardlydeflect the resilient part of the end trigger button in a manner tobypass the rib thus allowing depression of the end trigger button. Theneedle shroud may be arranged to inwardly support the resilient part ofthe end trigger button when in the initial position so as to preventdeflection. The inward support of the resilient part of the end triggerbutton is arranged to be removed on translation of the needle shroudinto the distal position. The end trigger button is biased in proximaldirection against the housing by a trigger spring. In this embodimentthe end trigger button may be hidden inside the distal end so only thelateral trigger button is operated by the user.

In yet another embodiment a wrap over sleeve trigger may be arrangedover the distal end. The sleeve trigger is translatable in longitudinaldirection between a distal position and a proximal position and has atleast one locking feature engageable with a respective mating part onthe needle shroud in the initial position so as to prevent depression ofthe sleeve trigger from the distal position into the proximal position.The mating part is arranged to be inwardly withdrawn by a cam feature ontranslation of the needle shroud into the distal position so as to allowthe sleeve trigger to be depressed. The end trigger button exhibits atleast one latch feature arranged to abut against a respective stop inthe housing so as to prevent depression of the end trigger button. Atleast one latch actuation boss on the sleeve trigger is arranged toinwardly deflect the latch feature disengaging it from the stop. The endtrigger button is biased in proximal direction against the housing by atrigger spring. A wrap over sleeve trigger may ease operation for userswith reduced dexterity.

The trigger spring and the shroud spring are specified to balance eachother's load. I.e. the relative strength of the shroud spring and thetrigger spring are arranged such that when the auto-injector is pressedagainst the injection site the shroud will always move first therebygiving a two step feel to the operation.

The screw thread of the first gear arrangement may end with a pitch ofzero on its proximal end allowing remaining torque in the torsion springto be released when the second gear member reaches the zero pitch.

According to another aspect of the invention a method for operating theauto-injector comprises the steps of:

-   -   grounding the first end of the torsion spring in the housing and        blocking the second gear arrangement in an initial state prior        to manual operation of the activating means,    -   releasing the second gear arrangement on manual operation of the        activating means so as to translate the plunger in proximal        direction for advancing the needle and supplying a dose of        medicament from the syringe under torque from the second end of        the torsion spring,    -   releasing the first end from the ground in the housing for        causing a translation through the first gear arrangement under        torque from the first end resulting in the needle getting        covered.

The first gear arrangement may translate the needle shroud in proximaldirection over the advanced needle on release of the first end from theground in the housing.

The needle shroud may be held in an initial position protruding from theproximal end of the housing in the initial state, wherein the needleshroud is interlocked to the activating means for preventing manualoperation in the initial state, wherein the needle shroud is translatedin distal direction into the housing into a distal position against theload of a shroud spring when pushed against the injection site. Theneedle shroud is rotationally fixed to the housing and to the secondgear member of the first gear arrangement. In the distal position theneedle shroud rotationally fixes a first gear member to the second gearmember of the first gear arrangement and releases the interlock so as toallow operation of the activating means.

The housing may have at least one viewing window for inspecting thesyringe.

The auto-injector may preferably be used for subcutaneous orintra-muscular injection, particularly for delivering one of ananalgetic, an anticoagulant, insulin, an insulin derivate, heparin,Lovenox, a vaccine, a growth hormone, a peptide hormone, a protein,antibodies and complex carbohydrates.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are not limitiveof the present invention, and wherein:

FIG. 1 is an isometric partial section of an auto-injector,

FIG. 2 shows longitudinal sections of the auto-injector in an initialstate,

FIG. 3 is a longitudinal section of the auto-injector after removal of aprotective needle shroud,

FIG. 4 is a detail view of a distal end of the auto-injector with atrigger button in the situation as in FIG. 3,

FIG. 5 is a detail view of the trigger button with an interlock featureto a needle shroud in the situation as in FIG. 3,

FIG. 6 is a longitudinal section of the auto-injector after depressionof the needle shroud,

FIG. 7 is an isometric detail view of a shroud follower locked inrotation to a shroud lead screw by depression of the needle shroud,

FIG. 8 is an isometric detail view of the interlock feature of FIG. 5disengaged by depression of the needle shroud,

FIG. 9 is a longitudinal section of the detail view of FIG. 8,

FIG. 10 is a longitudinal section of the auto-injector after depressionof the trigger button,

FIG. 11 is an isometric detail view of the trigger button prior todepression of the trigger button,

FIG. 12 is an isometric detail view of the trigger button afterdepression of the trigger button,

FIG. 13 is another isometric detail view of the trigger button afterdepression of the trigger button,

FIG. 14 is another isometric detail view of the trigger button prior todepression of the trigger button,

FIG. 15 is yet another isometric detail view of the trigger button afterdepression of the trigger button,

FIG. 16 is the auto-injector with a syringe advanced for needleinsertion,

FIG. 17 is the auto-injector with the emptied syringe,

FIG. 18 is the auto-injector on removal from the injection site afterthe syringe has been emptied,

FIG. 19 is a detail view in the situation as in FIG. 18 with the shroudlead screw released for rotation,

FIG. 20 is the auto-injector with the needle shroud fully advanced forpost injection needle safety,

FIG. 21 is a detail view of the shroud lead screw in the situation as inFIG. 20,

FIG. 22 is a detail view of the needle shroud locked in the position asin FIG. 20,

FIG. 23 is the auto-injector on removal from the injection site beforethe syringe has been emptied,

FIG. 24 is the auto-injector with the needle shroud fully advanced forpost injection needle safety after delivery of a partial dose,

FIG. 25 is an alternative embodiment of the auto-injector with a lateraltrigger button,

FIG. 26 is a detail view of an interlock mechanism between the lateraltrigger button, the needle shroud and the end trigger button with theneedle shroud depressed,

FIG. 27 is a detail view of the interlock mechanism with the lateraltrigger button depressed and the end trigger button released,

FIG. 28 is a detail view of the interlock mechanism with the end triggerbutton translated in proximal direction for releasing the plunger,

FIG. 29 is an alternative embodiment of the auto-injector with a wrapover sleeve trigger,

FIG. 30 is a detail view of an interlock mechanism between the sleevetrigger, the needle shroud and the end trigger button during an attemptto translate the sleeve trigger in proximal direction without priordepression of the needle shroud,

FIG. 31 is a detail view of locking features of the interlock mechanism,and

FIG. 32 is a sectional detail view of the locking features of theinterlock mechanism.

Corresponding parts are marked with the same reference symbols in allfigures.

DETAILED DESCRIPTION

FIG. 1 shows an isometric partial section of an auto-injector 1 with anelongate housing 2 and a needle shroud 3 for protecting a needle (notshown). A trigger button 4 (e.g., an activating member) arranged at adistal end D of the auto-injector 1 may be depressed in a proximaldirection P in order to trigger an automatic injection. The triggerbutton 4 is interlocked with the needle shroud 3 so it cannot be presseduntil the needle shroud 3 is pushed into the housing 2 by placing it onan injection site, e.g. a patient's skin and applying pressure. Theneedle shroud 3 has longitudinal splines 5 engaged in correspondinggrooves in the housing 2 for preventing relative rotation of the needleshroud 3 with respect to the housing 2

FIGS. 2a and 2b are longitudinal sections of the auto-injector 1 indifferent section planes approximately 90° offset from each other. Theauto-injector 1 is in an initial state prior to use. A syringe 7 ispartially surrounded and supported at a front end by a syringe carrier8. Attached at the front end of the syringe 7 is a hollow injectionneedle 19 for piercing a patient's skin and delivering a liquidmedicament stored inside the syringe 7 (syringe and needle are not shownin FIG. 2 b for clarity). Near the distal end of the syringe 7 a stopper10 is arranged for sealing and containing the medicament. The stopper 10may be advanced by a plunger 11 (e.g., a second gear member of a secondgear arrangement) in order to expel the medicament M from the syringe 7.The syringe carrier 8 is slidably arranged inside the needle shroud 3.The needle shroud 3 is biased towards a proximal end P by a shroudspring 12 in the shape of an integral compliant polymer beam elementintegrally moulded with the needle shroud 3 and acting against a firstrib 2.1 in the housing 2. The shroud spring 12 could likewise be of adifferent type, e.g. a compression spring.

The plunger 11 exhibits an external plunger lead screw 11.1 and isrotationally fixed to the housing 2 by a torque reaction rod 21 arrangedin an axial bore of the plunger 11. The axial bore and the torquereaction rod 21 both have a non-circular profile in order to keep theplunger 11 from rotating, e.g. a square profile or a profile with atleast one spline or flat. The torque reaction rod 21 is attached to thehousing 2 at the distal end D of the auto-injector 1 through a frameworkin a distal end cap 22 in such a manner that the torque reaction rod 21is prevented from rotating relative to the housing 2.

The plunger 11 is arranged inside a tubular plunger follower 15 (e.g., afirst gear member of the second gear arrangement), which is engaged tothe plunger lead screw 11.1 by at least one ball bearing (notillustrated). The plunger follower 15 is arranged inside a torsionspring 14 which in turn is arranged inside a tubular shroud lead screw13 (e.g., a first gear member of a first gear arrangement) with anexternal shroud lead screw thread 13.1. A tubular shroud follower 9(e.g., a second gear member of the first gear arrangement) is arrangedaround the shroud lead screw 13 and inside a distal part of the needleshroud 3. The shroud follower 9 is engaged to the shroud lead screw 13by at least one ball bearing (not illustrated).

The extension of the needle shroud 3 from the proximal end P is limitedby engagement of a pin 9.2 on the shroud follower 9 in a slot hole 3.3in the needle shroud 3. This engagement also fixes the shroud follower 9rotationally to the needle shroud 3. The shroud follower 9 is axiallyfixed to the tubular shroud lead screw 13 by the ball bearing.

Axial translation of the shroud lead screw 13 in the proximal directionP is prevented by an external lip 13.4 on the distal end of the shroudlead screw 13 abutting against a step 2.8 in the housing 2. Axialtranslation of the shroud lead screw 13 in the distal direction D isprevented by an internal flange 13.5 distally bearing against theproximal end of the plunger follower 15. The plunger follower 15 isaxially fixed to the housing 2 at its distal end. In the initial state,rotation of the shroud lead screw 13 is prevented by splined engagementwith the trigger button 4 (see FIG. 4). For this purpose the triggerbutton 4 has an inward boss 4.3 engaged between circumferential outwardbosses 13.3 on the shroud lead screw 13.

The torque from the proximal end 14.1 of the torsion spring 14 isresolved into the shroud lead screw 13. The torque from the distal end14.2 is resolved into the plunger follower 15. The torque from theplunger follower 15 is coupled through the ball bearing into an axialforce in the plunger 11. In the initial state, axial loads within theplunger 11 are resolved through into the housing 2 by means of a chassisclip arrangement at the distal end D. The chassis clip arrangementcomprises two resilient chassis clips 16 fixed to the housing 2. Thechassis clips 16 are engaged proximally behind a shoulder 11.2 in theplunger 11 in a manner to prevent translation of the plunger 11 inproximal direction P. Due to ramped engagement the shoulder 11.2 istrying to flex the chassis clips 16 outwards which is prevented by twotrigger beams 4.1 on the trigger button 4 respectively arranged betweenan outward pin on the chassis clip 16 and a rigid support beam 17.

The trigger button 4 is locked in a distal position in the initial stateto prevent unintended activation of the auto-injector 1. Flexible firstbeam elements 2.2 integrally moulded with the housing 2 obstruct themotion of the trigger button 4 if attempts are made to depress it (seeFIGS. 5, 8). The first beam elements 2.2 are deflected out of the pathof the trigger button 4 by a second beam element 3.1 on the needleshroud 3 on axial movement of the needle shroud 3 within the housing 2(see FIGS. 8, 9) in distal direction D. This is achieved when theproximal end P is pressed against the injection site.

In the as delivered initial state a protective needle shield 18 isarranged on the injection needle 19.

A sequence of operation is as follows:

The user removes the protective needle shield 18 from the needle 19.This can be achieved by a device cap engaged with the needle (notillustrated). The needle 19 is a safe distance back within the needleshroud 3 to protect the user from accidental needle stick injuries (seeFIG. 3).

The user places and pushes the proximal end P of the auto-injector 1 onthe injection site, e.g. a patient's skin. The needle shroud 3 moves indistal direction D into the housing 2 by a small distance (see FIG. 6).Due to the slot hole 3.3 this translation does not translate the shroudfollower 9. The translating second beam element 3.1 flexes the firstbeam elements 2.2 outwards thus clearing the path for the trigger button4 and releasing the aforementioned interlock (see FIGS. 8, 9). Themoulded shroud spring 12 opposes this motion but is specified such thatits spring rate and preload are low enough for this to feel natural. Aresilient third beam element 3.2 on the needle shroud 3 is deflectedinwards by contact with a ramped second rib 2.3 on the housing 2 ontranslation of the needle shroud 3. The third beam element 3.2 deflectsa fourth beam element 9.1 on the shroud follower 9 into a spline 13.2 onthe shroud lead screw 13 (see FIGS. 4, 7).

As the shroud follower 9 is rotationally fixed to the housing 2 throughits engagement with the needle shroud 3, the fourth beam element 9.1provides further grounding of the shroud lead screw 13 to the housing 2.As detailed above, the shroud lead screw 13 is already grounded to thehousing 2 through a splined engagement with the trigger button 4.

When ready to do so, the user depresses the trigger button 4,translating it in proximal direction P (see FIGS. 10, 12, 13, 15). Thetrigger beams 4.1 on the trigger button 4 are translated with thetrigger button 4 in a manner to allow the outward pin 16.1 to enter anaperture 4.2 in the trigger beam 4.1 by the chassis clip 16 being flexedoutwards due to ramped engagement with the shoulder 11.2 under the forcepulling the plunger 11 in proximal direction P.

The plunger 11 moves in proximal direction P towards the stopper 10driven by rotation of the plunger follower 15. As stated, the plunger 11is prevented from rotating by the torque reaction rod 21 down itscentre. This could be achieved with one or more splines, flats or byusing a square shaft as shown in this embodiment. One or more ballbearings provide a low friction contact between the plunger follower 15and the plunger lead screw 11.1. Depression of the trigger button 4 alsoremoves the splined engagement of the trigger button 4 from the shroudlead screw 13 by translating the inward boss 4.3 out of engagement withthe circumferential outward bosses 13.3 (see FIG. 15). Now, the shroudlead screw 13 is grounded to the housing 2 through the shroud follower 9only. This means at any point from now, a shroud extension mechanismdescribed below would be triggered if the auto-injector 1 is removedfrom the injection site, thereby ensuring the needle 19 is covered. Thetrigger button 4 is locked in a fully depressed position by snaps 4.4acting against the housing 2 (see FIGS. 13 and 15).

The plunger 11 drives the syringe 7 forward by pushing on the stopper 10thus inserting the needle 19 into the injection site. The subcutaneousinjection depth is set by a rear flange 8.1 on the syringe carrier 8contacting a stop 2.4 in the housing 2 (see FIG. 16).

When the injection depth has been reached the stopper 10 is drivenforwards in proximal direction P within the syringe 7, injecting thedose of medicament M. The stopper 10 continues to move until it reachesthe end of the syringe 7 thereby fully emptying the syringe 7. Thiswould require the user to hold the auto-injector 1 in place for asufficient period of time. In this embodiment, the user is asked to keeppressure on the injection site for a short period of time (e.g.approximately 10 seconds), which can be communicated to the user throughuser instructions. Other options would be observance of movingcomponents within the auto-injector 1, or an audible ratchet detectingmovement of the plunger 11.

After confirmation that the full dose has been delivered, the userwithdraws the auto-injector 1 from the injection site. With withdrawal,the needle 19 is extracted from the skin, and the needle shroud 3extends under the force of the shroud spring 12 (see FIG. 18). The thirdbeam element 3.2 is translated back in proximal direction P thus nolonger deflecting the fourth beam element 9.1 inwards. Hence the fourthbeam element 9.1 flexes outwards again and disengages the shroudfollower 9 from the shroud lead screw 13. Therefore torque within theshroud lead screw 13 is no longer resolved through to the housing 2 (seeFIG. 19). With the grounding to the housing 2 removed, the torque is nowresolved through the ball bearing interface to an axial force on theshroud follower 9. Further movement of the plunger 11 in the proximaldirection P is not possible in this situation, so when the shroudfollower 9 is released it moves in the proximal direction P pushing theneedle shroud 3 further out of the proximal end P of the housing 2 thuscompletely covering the needle 19 (see FIG. 20). The shroud lead screwthread 13.1 ends with a pitch of zero on the proximal end allowing anyremaining torque in the torsion spring 14 to be released (see FIG. 21).This makes the auto-injector 1 tamper proof post injection, e.g. if theuser tries to dismantle the auto-injector 1.

The needle shroud 3 is locked in this extended position by snaps 2.5within the case 2 (see FIG. 22).

FIG. 23 illustrates removal from skin mid injection with the syringe 7only partially emptied. As the shroud follower 9 disengages from theshroud lead screw 13, the torque within the shroud lead screw 13 is nolonger resolved through to the housing 2 but through the ball bearinginterface to an axial force on the shroud follower 9. Although thetorque from the distal end 14.2 of the torsion spring 14 is stillresolved through the plunger 11, the torque required to extend theneedle shroud 3 is less than the torque required to forward the plunger11, hence the distal end 14.2 becomes ground.

FIG. 24 shows the auto-injector 1 with the needle shroud 3 fullyadvanced for post injection needle safety after delivery of the partialdose. The zero end pitch of the shroud lead screw thread 13.1 allows thetorsion spring 14 to be released preventing further drug delivery.

FIG. 25 shows an alternative embodiment of the auto-injector 1 with alateral trigger button 20 (e.g., an activating member). The lateraltrigger button 20 is an integral part of the housing 2. It may bemoulded orthogonal to the housing 2 and then folded into place. However,the auto-injector 1 also comprises the end trigger button 4 of theembodiment illustrated in FIGS. 1 to 24, but hidden inside the distalend D closed by the distal cap 22 attached to the housing 2. A triggerspring 23 in the shape of a small compression spring applies a loadbetween the distal cap 22 and the trigger button 4.

The sequence of operation is as described above for the embodiment inFIGS. 1 to 24 except in the following steps:

The initial position and function of all components is identical withthe exception of the button interlock. The lateral trigger button 20 islocked in an extended position in the initial state to preventunintended activation of the auto-injector 1. A boss 20.1 on the distalend of the lateral trigger button 20 extends through an aperture in thehousing 2. In the initial state the boss 20.1 abuts against one of theinward bosses 4.3 on the end trigger button 4 which is inwardlysupported by the shroud lead screw 13 and by a distal extension 3.4 onthe needle shroud 3 arranged between the inward boss 4.3 and the shroudlead screw 13. Any force applied to the lateral trigger button 20 istherefore statically resolved preventing its depression. The inward boss4.3 on the end trigger button 4 abuts against a third rib 2.6 in thehousing 2 in proximal direction P thus preventing release of the endtrigger button 4. When the auto-injector 1 is pressed against the skin,the needle shroud 3 translates within the housing 2 and a window 3.5 inthe distal extension 3.4 becomes aligned with the boss 20.1 (see FIG.26) allowing the lateral trigger button 20 to be depressed (see FIG. 27)thereby flexing the inward boss 4.3 inwards into the window 3.5 in sucha manner that the inward boss 4.3 comes clear of the third rib 2.6releasing the end trigger button 4 which is then translated under theaction of the trigger spring 23 (see FIG. 28). This releases the chassisclip 16 resolving the axial load on the plunger 11 as in the embodimentin FIGS. 1 to 24.

FIG. 29 shows another alternative embodiment of the auto-injector 1 witha wrap over sleeve trigger 24 (e.g., an activating member) arranged overthe distal end D and extending over roughly half the length of thehousing 2. However, the auto-injector 1 also comprises the end triggerbutton 4 of the embodiment illustrated in FIGS. 1 to 24, but hiddeninside the distal end D. A trigger spring 23 applies a load between thesleeve trigger 24 and the end trigger button 4. The load from thetrigger spring 23 is balanced by load from the shroud spring 12. The endtrigger button 4 exhibits latch features 4.5 initially abutted against astop 2.7 in the housing 2 (see FIGS. 29 to 32).

The sequence of operation is as described above for the embodiment inFIGS. 1 to 24 except in the following steps:

The initial position and function of all components is identical withthe exception of the button interlock. Movement of the trigger sleeve 24is prevented to avoid unintended activation of the auto-injector 1. Ifthe trigger sleeve 24 is moved, a locking feature 24.1 engages with amating part 3.6 on the needle shroud 3 guarding against the usergrabbing the housing 2 and attempting to operate the trigger sleeve 24(see FIG. 30). When the auto-injector 1 is pressed against the skin, theneedle shroud 3 translates within the housing 2 and the mating part 3.6on the shroud 3 is inwardly withdrawn as the resilient third beamelement 3.2 runs down a cam on the second rib 2.3 in the housing 2allowing it to be depressed.

When ready to do so, the user translates the sleeve trigger 24 inproximal direction P. As the trigger sleeve 24 translates, a latchactuation boss 24.2 on the sleeve trigger 24 deflects the latch feature4.5 inwards disengaging it from the stop 2.7 in the housing 2. The endtrigger button 4 is then translated under the action of the triggerspring 23. This releases the chassis clip 16 resolving the axial load onthe plunger 11.

This allows for a forced activation sequence. The intended activation ofthe auto-injector 1 involves the needle shroud 3 (skin interlock) beingdepressed prior to the trigger sleeve 24 being translated. Both parts(needle shroud 3 and trigger sleeve 24) are sprung relative to thehousing 2 in this embodiment. By careful selection of the springproperties of the shroud spring 12 and the trigger spring 23, thecorrect sequence can be achieved. If the shroud spring 12 is less stiffthan the trigger spring 23, it will compress first when a load isapplied between the needle shroud 3 and the trigger sleeve 24. In thecase of an end trigger button 4 only as in FIGS. 1 to 24, this is notrequired as the user holds the housing 2 and is able to move the twoparts independently.

The embodiment of FIGS. 29 to 32 furthermore allows for a non-returnactivation sequence, i.e. the embodiment allows the needle shroud 3 tobe depressed and the trigger sleeve 24 to be moved up to the point ofrelease of the end trigger button 4 and then released without changingthe load paths within the auto-injector 1. I.e. the auto-injector 1 canbe placed on the skin and then removed and remain in a safe state. Oncethe trigger sleeve 24 moves beyond the point of release of the internalend trigger button 4, the auto-injector 1 is activated under the actionof the trigger spring 23 and cannot be stopped by the user. Thisprevents the user partially activating the auto-injector 1 and leavingit in a partially activated state, which would result in theauto-injector firing immediately on the next attempt without requiringthe sequenced operation.

Furthermore the embodiment demonstrates the ability to convert theauto-injector 1 from an end trigger (FIGS. 1 to 24) to a sleeve trigger(FIGS. 29 to 32) by adding an additional part, thus achieving a platformdesign.

The auto-injector 1 may preferably be used for delivering one of ananalgetic, an anticoagulant, insulin, an insulin derivate, heparin,Lovenox, a vaccine, a growth hormone, a peptide hormone, a protein,antibodies and complex carbohydrates.

The invention claimed is:
 1. An auto-injector for administering a doseof a liquid medicament, comprising: an elongate housing arranged tocontain a syringe with a hollow needle and a stopper for sealing thesyringe and displacing the medicament, the elongate housing having adistal end and a proximal end with an orifice intended to be appliedagainst an injection site, wherein the syringe is slidably arranged withrespect to the housing, a single torsion spring capable of, uponactivation, pushing the needle from a covered position inside thehousing into an advanced position through the orifice and past theproximal end, operating the syringe to supply the dose, and covering theneedle on removal of the auto-injector from the injection site, anactivating member arranged to lock the torsion spring in a pressurizedstate prior to manual operation and capable of, upon manual operation,releasing the torsion spring for injection, a first gear arrangementarranged for converting torque from a proximal end of the torsion springinto a translative force, and a second gear arrangement arranged forconverting torque from a distal end of the torsion spring into atranslative force, the proximal end of the torsional spring beingdifferent than the distal end of the torsional spring, wherein theproximal end of the torsion spring is arranged to be grounded in thehousing while the distal end of the torsion spring is configured to acton a plunger through the second gear arrangement for advancing theneedle and supplying the dose, wherein the activating member is arrangedto block or release the second gear arrangement, and wherein the distalend of the torsion spring is configured to be grounded in the housingwhile the proximal end of the torsion spring is releasable from itsground in the housing to act on the first gear arrangement for causing atranslation through the first gear arrangement resulting in the needlegetting covered.
 2. The auto-injector according to claim 1, furthercomprising a clip arrangement comprising at least one resilient chassisclip attached to the housing, the at least one chassis clip engageableproximally behind a shoulder in the plunger in a manner to preventtranslation of the plunger in a proximal direction, wherein the shoulderis arranged to flex the at least one chassis clip outwards due to rampedengagement when a force in the proximal direction is applied to theplunger, wherein the activating member comprises an end trigger buttonarranged at the distal end translatable between a distal position and aproximal position, wherein at least one trigger beam is arranged on thetrigger button in a manner to outwardly support the at least one chassisclip to prevent it from being outwardly deflected when the end triggerbutton is in the distal position, and wherein the at least one triggerbeam is arranged to be repositioned on translation of the end triggerbutton into the proximal position in a manner to allow outwarddeflection of the at least one chassis clip.
 3. The auto-injectoraccording to claim 2, further comprising: a needle shroud arranged to bein an initial position protruding from the proximal end of the housing,and a wrap over sleeve trigger is arranged over the distal end of thehousing, the sleeve trigger translatable in a longitudinal directionbetween a distal position and a proximal position, the sleeve triggerhaving at least one locking feature engageable with a respective matingpart on the needle shroud in the initial position so as to preventdepression of the sleeve trigger from the distal position into theproximal position, wherein the mating part is arranged to be inwardlywithdrawn by a cam feature on translation of the needle shroud into thedistal position so as to allow the sleeve trigger to be depressed,wherein the end trigger button comprises a latch feature arranged toabut against a respective stop in the housing so as to preventdepression of the end trigger button, and wherein at least one latchactuation boss on the sleeve trigger is arranged to inwardly deflect thelatch feature disengaging it from the stop, wherein the end triggerbutton is biased in the proximal direction against the housing by atrigger spring.
 4. The auto-injector according to claim 3, wherein thetrigger spring and the shroud spring are specified to balance eachother's load.
 5. The auto-injector according to claim 2, furthercomprising: a needle shroud arranged in the housing surrounding thesyringe and translatable in a longitudinal direction, and at least oneflexible first beam element arranged on the housing, the at least oneflexible first beam element arranged to obstruct a path of the endtrigger button so as to prevent its depression, wherein a second beamelement is arranged on the needle shroud in a manner to deflect theflexible first beam element out of the path of the end trigger button ondepression of the needle shroud.
 6. The auto-injector according to claim2, further comprising: a needle shroud arranged to be in an initialposition protruding from the proximal end of the housing and arranged tobe translated in a distal direction into the housing into a distalposition, and a third rib arranged in the housing in a manner toobstruct a path of a resilient part of the end trigger button so as toprevent its depression, wherein a lateral trigger button is laterallyarranged on the housing arranged to inwardly deflect the resilient partof the end trigger button in a manner to bypass the third rib thusallowing depression of the end trigger button, wherein the needle shroudis arranged to inwardly support the resilient part of the end triggerbutton when in the initial position so as to prevent deflection, whereinthe inward support of the resilient part of the end trigger button isarranged to be removed on translation of the needle shroud into thedistal position, and wherein the end trigger button is biased in theproximal direction against the housing by a trigger spring.
 7. Theauto-injector according to claim 1, wherein the first gear arrangementand the second gear arrangement respectively comprise a first gearmember coupled to the respective end of the torsion spring, wherein thefirst gear member is engaged through a respective screw thread to arespective second gear member arranged to translate on rotation of thefirst gear member.
 8. The auto-injector according to claim 7, furthercomprising a needle shroud arranged to be in an initial positionprotruding from the proximal end of the housing in an initial stateinterlocked to the activating member for preventing manual operation,wherein the needle shroud is arranged to be translated in a distaldirection into the housing into a distal position against a load of ashroud spring when pushed against the injection site, wherein the needleshroud is rotationally fixed to the housing and to the second gearmember of the first gear arrangement, and wherein in the distal positionthe needle shroud is arranged to rotationally fix the first gear memberto the second gear member of the first gear arrangement and to allowoperation of the activating member.
 9. The auto-injector according toclaim 8, wherein the activating member is arranged to be in a splinedengagement with the first gear member of the first gear arrangement inthe initial state so as to rotationally fix the first gear member to thehousing, and wherein the activating member is arranged to remove thissplined engagement on manual operation.
 10. The auto-injector accordingto claim 7, wherein the screw thread ends with a pitch of zero on itsproximal end allowing remaining torque in the torsion spring to bereleased when the second gear member reaches the zero pitch.
 11. Theauto-injector according to claim 1, further comprising a needle shroudarranged in the housing surrounding the syringe and translatable in alongitudinal direction, wherein the needle shroud is coupled to thefirst gear arrangement in a manner to be translated in a proximaldirection over the needle in the advanced position on release of thefirst proximal end of the torsion spring from its ground in the housing.12. The auto-injector according to claim 11, wherein a torque requiredto advance the needle shroud is less than a torque required to advancethe plunger and the stopper.
 13. The auto-injector according to claim 1,further comprising a needle shroud arranged in the housing surroundingthe syringe and translatable in a longitudinal direction, wherein thefirst gear arrangement comprises a shroud lead screw and a shroudfollower engaged with the proximal end of the torsion spring andthreadedly engaged with the shroud lead screw such that rotation of theshroud follower is configured to cause axial translation of the shroudlead screw.
 14. The auto-injector of claim 13, wherein the shroudfollower is axially fixed to the housing.
 15. The auto-injectoraccording to claim 1, wherein the second gear arrangement comprises theplunger and a plunger follower engaged with the distal end of thetorsion spring and threadedly engaged with the plunger such thatrotation of the plunger follower is configured to cause axialtranslation of the plunger.
 16. The auto-injector of claim 15, whereinthe plunger follower is axially fixed to the housing.
 17. Theauto-injector according to claim 1, wherein the torsion spring isconfigured to exert a torque to push the needle from the coveredposition inside the housing into the advanced position through theorifice and past the proximal end, to supply the dose from the syringe,and to cover the needle on removal of the auto-injector from theinjection site when the torsion spring is activated.
 18. Theauto-injector of claim 1, wherein the torsion spring is configured suchthat a torque to cover the needle is less than a torque to advance theplunger when the distal end of the torsion spring is grounded in thehousing.
 19. The auto-injector of claim 1, wherein the first geararrangement comprises a beam element configured to ground the proximalend of the torsion spring in the housing, and be deflected to releasethe ground of the proximal end of the torsion spring from the housing toenable the torque from the proximal end of the torsion spring to beconverted to a translative force on a shroud of the first geararrangement.